This invention relates to compositions of matter useful as developing agents in the manufacture of integrated circuits and other semi-conductor derived circuitry elements made by either additive or subtractive processes. More particularly, it relates to developer agents for use in the semiconductor industry which contain methyl triethanolammonium ions. More particularly, it relates to solutions of developer agents for use in the semiconductor industry which contain methyl triethanolammonium hydroxide, which may also be referred to as tris(2-hydroxyethyl) methylammonium hydroxide.
Integrated circuits are typically constructed by depositing a series of individual layers of predetermined materials on a wafer shaped semiconductor substrate, or xe2x80x9cwaferxe2x80x9d. The individual layers of the integrated circuit are in turn produced by a series of manufacturing steps. For example, in forming an individual circuit layer on a wafer containing a previously formed circuit layer, an oxide, such as silicon dioxide, is deposited over the previously formed circuit layer to provide an insulating layer for the circuit. A pattern for the next circuit layer is then formed on the wafer using a radiation alterable material, known as photoresist. Photoresist materials are generally composed of a mixture of organic resins, sensitizers and solvents. Sensitizers are compounds, such as diazonapthaquinones, that undergo a chemical change upon exposure to radiant energy, such as visible and ultraviolet light resulting in an irradiated material having differing salvation characteristics with respect to various solvents than the non-irradiated material. Resins are used to provide mechanical strength to the photoresist and the solvents serve to lower the viscosity of the photoresist so that it can be uniformly applied to the surface of the wafers. After a photoresist layer is applied to the wafer surface, the solvents are evaporated and the photoresist layer is hardened, usually by heat treating the wafer. The photoresist layer is then selectively irradiated by placing a radiation opaque mask containing a transparent portion defining the pattern for the next circuit layer over the photoresist layer and then exposing the photoresist layer to radiation. The photoresist layer is then exposed to a chemical, known as developer, in which either the irradiated or the non-irradiated photoresist is soluble and the photoresist is removed in the pattern defined by the mask, selectively exposing portions of the underlying insulating layer. The exposed portions of the insulating layer are then selectively removed using an etchant to expose corresponding sections of the underlying circuit layer. The photoresist must be resistant to the etchant, so as to limit the attack of the etchant to only the exposed portions of the insulating layer. Alternatively, the exposed underlying layer(s) may be implanted with ions which do not penetrate the photoresist layer thereby selectively penetrating only those portions of the underlying layer not covered by the photoresist. The remaining photoresist is then stripped using either a solvent, or a strong oxidizer in the form of a liquid or a gas in the plasma state. The next layer is then deposited and the process is repeated until fabrication of the semiconductor device is complete.
Choline (2-hydroxyethyltrimethylammonium hydroxide), bis(2-hydroxyethyl) dimethylammonium hydroxide, and tris(2-hydroxyethyl)methylammonium hydroxide are known photoresist stripping agents used in the printed circuitboard (xe2x80x9cPCBxe2x80x9d) industry. Only choline and tetramethylammonium hydroxide are known to be used as developing agents in the semiconductor manufacture. However, these ammonium hydroxides are not thermally stable, and they tend to release amine vapor due to thermal decomposition during the developing process. This amine vapor can react or become mixed with an essential chemical used in the processing of a semi-conductor based circuit element to form unwanted deposits in the chemical vapor deposition chamber if it is not completely removed from the processing area. Thus, tight engineering controls must be constantly employed to remove these amine vapors. If a composition were available which functioned adequately as a developer, and which did not release appreciable amounts of amine vapor during a developing process in which it was employed, such composition would represent an advance in the art of semi-conductor developers. The present invention provides such a developer.
The present invention provides compositions useful as a developing agents in processing semi-conductor based circuit elements and precursors thereof comprising an aqueous or alcoholic solutions of tris-(2-hydroxyethyl)methylammonium hydroxide, either alone, or more preferably in combination with a stabilizer such as N-hydroxyethyl ethylenediamine.
The present invention provides a chemical composition which can be used as a developing agent in the semiconductor processing industry. A developer composition according to the invention comprises tris-(2-hydroxyethyl)methylammonium hydroxide, which significantly reduces the amount of volatile amine generated during the developing process. The generation of a reduced amount of volatile amines during the developing process greatly reduces the level at which internal atmospheric control equipment must operate to remove such undesirable amines from the process area.
The tris-(2-hydroxyethyl)methylammonium hydroxide useful in accordance with the present invention is exemplified by the chemical structure: 
and may be produced by a conventional alkoxylation process according to the general reaction: 
by reacting methyl diethanolamine with ethylene oxide in the presence of water to provide an aqueous solution of tris-(2-hydroxyethyl)methylammonium hydroxide having a strength which is variable by controlling the concentration of the starting materials, as is well-known in the art of alkoxylation using ethylene oxide. Typically, an aqueous solution of tris-(2-hydroxyethyl)methylammonium hydroxide may be prepared having a concentration of between about 10.00 and 80.00% by weight based on the total solution weight, including every hundredth percentage therebetween. By dilution with water, any concentration of tris-(2-hydroxyethyl)methylammonium hydroxide below 80.00% may be achieved. It is most preferred that a developer solution according to the invention contain tris-(2-hydroxyethyl)methylammonium hydroxide in any percentage by weight based upon the total weight of the developer solution between 10.00% and 70.00%, including every hundredth percentage therebetween.
Tris-(2-hydroxyethyl)methylammonium hydroxide shows an unexpected result of being considerably more thermally stable than both choline and bis-(2-hydroxyethyl) dimethyl ammonium hydroxide when employed under conditions normally encountered in the development of semi-conductor derived circuitry elements or precursors thereof. While described above as being aqueous solutions, the developers according to the invention may also comprise tris-(2-hydroxyethyl)methylammonium hydroxide in alcohol solution, such as a C1-C6 alcohol, including without limitation methanol and ethanol, merely by conducting the alkoxylation reaction in the selected alcohol, or an aqueous solution of the alcohol.
It is clear that the tris-(2-hydroxyethyl)methylammonium hydroxide of the invention: 
differs from bis-(2-hydroxyethyl) dimethylammonium hydroxide 
and from choline 
by the number of methyl groups and hydroxy ethyl groups bonded to the nitrogen atom in the quaternary amine.